This invention relates to discharge tube apparatus and, more particularly, to apparatus in which it is wished to maintain a temperature difference between parts of the tube.
Many gas discharge tubes used in laser oscillators or amplifiers require a laser amplifying medium of ionized gas to be kept at a high temperature, in the region of two thousand degrees Celsium whilst having the amplifying medium contained within a vessel, the walls of which would deteriorate at such high temperatures and must thus be kept at a lower temperature. One way in which this has previously been done is to arrange a structure having low thermal conductivity between the amplifying medium and the vessel walls, as illustrated in FIGS. 1 and 2 of the accompanying drawings which are transverse and longitudinal sections respectively of part of a laser discharge tube suitable for copper or gold vapour lasers. The containing vessel 1 of quartz, which can withstand temperatures of only about 1000.degree. C., contains the laser amplifying medium, which typically is a metal vapour and a buffer gas, which must be maintained at a suitably high temperature for laser action to occur. The temperature of the amplifying medium depends upon the metal vapour used and may be up to 2000.degree. C. in some cases. A thermally insulating tube 3 is located coaxially within the vessel 1 to enable a suitable temperature difference to be maintained between the vessel 1 and the amplifying medium 2. The tube 3 is of a sandwich construction, typically having an outer alumina layer 4, an adjacent layer of zirconia felt 5, and an inner layer 6 of alumina. In some applications it may be desirable to include an additional coating 7 of tantalum between the outer layer 4 and the quartz vessel 1.